Method and device for controlling critical switch failure and neutral conditions at high and low vehicle speeds

ABSTRACT

A control system for controlling automatic shifting of a manual/automatic transmission is disclosed including a cruise control system and an auto-shift mode for controlling automatic upshift and downshift operations between the top two gears of a heavy duty truck transmission. Certain failures of equipment or incorrect driving habits of operators are corrected for with algorithms which prevent undesirable operating conditions which compromise the acceptability of an electronically controlled heavy duty truck transmission equipped vehicle. The mechanism by which auto-shift operation of the transmission is requested is also compared with parameters such as vehicle speed and engine speed in order to determine whether gears should be engaged or disengaged, the gears being those subject to auto-shift control of the system controller.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to automatic and manual/automatic transmissionsand more particularly to motor vehicles including such transmissions anddevices for detecting and preventing undesirable operating conditionsduring vehicle operation as a result of critical equipment failures.

The present invention relates to control systems and methods ofoperation for manual/automatic heavy duty transmission systems whereingear ratio selection and gear shift timing decisions are made and/orexecuted based upon measured and calculated parameters such asengagement condition of the transmission, vehicle or transmission outputshaft speed, transmission input shaft speed, engine speed, throttleposition, and the like. Until recently, transmissions, particularly forheavy duty applications, have historically been the manual shift typerequiring actuation of a clutch and gear shift lever by the driver inorder to change final drive gear ratios. Gear ratio selection isaccomplished using a shift lever coupled to the transmission formechanically disengaging and engaging various gear ratio operationstates of the transmission. Due to the large number of gear ratiooperation states associated with compound transmissions or transmissionshaving a splitter type auxiliary section, a great deal of effort isrequired to manually shift throughout the entire set of available gearratio operation states of the transmission. More recently, successfuldevices which combine manual and automatic shifting operation undercertain conditions have been developed such as the invention disclosedin U.S. Pat. No. 4,722,248, the disclosure of which is incorporatedherein by reference.

When an electronic shift control system is coupled to a manual/automatictransmission, a lessening of operator fatigue and improved fuel economyresult. A device which combines manual shifting of low vehicle speedgear ratios with automatic shifting between sequentially related highervehicle speed gear ratios, and more particularly between the "top two"available gear ratios of the manual/automatic transmission, reducesdriver fatigue. By providing for automatic gear selection of the twohighest gear ratio operation states of the transmission, or the "toptwo" gears, an automatic shift schedule can be developed for increasingfuel economy. Additionally, an automatic gear shift device can be usedin conjunction with cruise control electronic systems compatible withheavy duty truck applications.

One special attention situation that arises, in the case of amanual/automatic transmission controlled by an electronic controllerincluding cruise control algorithms and algorithms for shifting the "toptwo" gears, is sensor failure. When the "top gear" switch, or theelectronic sensing device that indicates the driver is requestingautomatic shift mode fails, special condition operating conditions mayexist or arise. More particularly, the "top gear" switch may fail closedindicating that the driver is requesting automatic gearshift operationwhen in actuality the switch is open or the switch is in the openposition according to the actuator lever, yet the contacts remain fusedtogether. Another switch failure state occurs when the switch contactswill not close, thus providing a stimulus to the electronic controllerwhich responds and disengages automatically engaged auto-shift gearsthereby allowing a vehicle to remain in neutral and increase in speedwithout engaging one of the auto-shift selectable transmission gears toenable engine-drag braking of the vehicle. When the "top gear" switchfails open, the auto-shift mode cannot be enabled. Thus, an undesirableoperating condition arises when a vehicle is traveling downhill at thetime and the transmission remains in neutral after the driver hasrequested automatic gear selection operation.

Another undesirable state occurs when the switch fails closed, i.e.,auto-shift mode is requested at all times, and the transmission remainsin one of the top two gears even though the vehicle slows down below apredetermined speed. This condition may occur when the vehicle is comingto a stop or encounters an incline and the vehicle slows as a result ofthe incline. Lower gear selection becomes impossible if the switch isfailed closed, and the control system will not disengage auto-shift modegear engagement, and thus the vehicle engine may stall due to impropergear ratio selection. An additional issue exists when the driverintentionally allows the vehicle to coast downhill in neutral to achievehigher vehicle speeds than the normal road speed governor of the vehicleengine will allow.

A control system for controlling a cruise control system and anassociated heavy duty truck transmission having at least twoautomatically selectable gear ratio operational states is needed whichincludes algorithms for avoiding the conditions which exist due tocomponent failure or certain driver practices that create undesirableoperating conditions.

SUMMARY OF THE INVENTION

A device for controlling gear engagement/disengagement of amanual/automatic transmission coupled to an engine, according to oneembodiment of the present invention, is disclosed wherein thetransmission operates in a manual mode of operation wherein a pluralityof gear ratio operation states are selectable according to a mechanicaldriver input, and wherein the transmission also operates in an automaticmode of operation wherein first and second automatically engagable gearratio operation states and a neutral operation state are selectable bythe device when the transmission is placed in an automatic mode ofoperation, wherein the device comprises shift means connected to thetransmission for selecting between manual mode and automatic mode ofoperation of the transmission, means for producing a top gear signalwhen the shift means is in the automatic mode of operation position,means for sensing vehicle speed and producing a speed signalcorresponding to vehicle speed, means for producing a gear engagementsignal in response to the top gear signal or when the speed signal iswithin a predetermined range, and means for engaging one of the first orsecond automatically engageable gear ratio operation states of thetransmission in response to the gear engagement signal.

A method for controlling gear engagement/disengagement of amanual/automatic transmission coupled to an engine, according to anotherembodiment of the present invention, is disclosed wherein thetransmission includes gear shift means, a manual mode of operationwherein a plurality of gear ratio operation states are selectableaccording to driver positioning of the shift means, and an automaticmode of operation wherein first and second automatically engagable gearratio operation states and a neutral operation state are automaticallyselectable when the shift means is positioned in an automatic modeposition, the method comprising the steps of selecting between manualmode and automatic mode of operation of the transmission, producing atop gear signal when the shift means is in the automatic mode ofoperation position, sensing vehicle speed and producing a speed signalcorresponding to vehicle speed, producing a gear engagement signal inresponse to the top gear signal or when the speed signal is within apredetermined range, and engaging one of the first or second gear ratiooperation states of the transmission in response to the gear engagementsignal.

One object of the present invention is to provide an improvedmanual/automatic transmission shift control system.

Another object of the present invention is to prevent undesirableoperating conditions which may arise as a result of equipment failure orcertain acts of drivers.

A further object of the present invention is to control the transmissionto automatically shift into one of the "top two" gears whenever vehiclespeed exceeds a particular threshold.

These and other objects of the present invention will become moreapparent from the following description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an electronic controllerconsistent with the teachings of the present invention.

FIG. 2 is a diagrammatic illustration of one embodiment of the enginecontrol module to manual/automatic transmission control interface.

FIG. 3 is another embodiment of the control interface between enginecontrol module and transmission of FIG. 1.

FIG. 4 is a diagrammatic illustration of the shift pattern for a DanaSpicer 7-speed heavy duty truck transmission.

FIG. 5 is a diagrammatic illustration of an Eaton Fuller heavy dutytruck transmission shift pattern.

FIG. 6 is a diagrammatic illustration of a control system which includesthe controller of FIGS. 1 and 2.

FIG. 6A is an alternate embodiment of the transmission interface shownin FIG. 6 and which corresponds to the transmission interface depictedin FIG. 3.

FIG. 7 is a flowchart of an auto-shift sequence according to the presentinvention.

FIG. 8 is a more detailed flowchart of a portion of the auto-shiftsequence according to the present invention.

FIG. 9 is a more detailed flowchart of a portion of the auto-shiftsequence according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIG. 1, a diagrammatic illustration of a control system15 according to the present invention is shown. The control system 15includes as its central component electronic control module (ECM) 20.ECM 20 is a microcomputer including a microprocessor having ROM and RAMand a plurality of inputs and outputs (I/O) in addition to interfacecircuits for I/O interfacing. The input signals supplied to ECM 20 areproduced by various switches and sensors which respond to operatingconditions and inputs from the driver.

Switch SW3, a normally open switch, provides an input to ECM 20indicating when brake pedal 32 has been depressed or actuated. Brakepedal 32 is mechanically linked to switch SW3 via linkage 34. The signalfrom switch SW3 supplied to ECM 20 is normally a logic low as a resultof resistor R1 pulling input IN1 of ECM 20 to ground or logic low whenswitch SW3 is in the open state. Switches SW1 and SW2 are mounted in thedriver's cab or driver compartment and provide the driver with a meansfor turning the cruise control functions on and off, via switch SW2, andfor establishing a desired cruise speed via switch SW1, as well aspermitting the vehicle to coast without cruise control operation. SwitchSW1 also provides input signals to activate resume/acceleration featureswell known in the art of cruise control systems. Switch SW2 enablescruise control operation while switch SW1 is used to activate theoperational modes of the cruise control system built into the softwareof ECM 20. Switch SW1 is a momentary center-off SPDT switch. Theset/coast cruise control function is activated by shorting input IN3 ofECM 20 to logic high voltage, or +V_(DC). This is accomplished byclosing switch SW1 and connecting +V_(DC) to the signal path connectedto resistor R3 and input IN3. In the alternative, when switch SW1 isactuated to connect input IN4 and resistor R5 with +V_(DC), input IN4 israised to a logic high and the ECM 20 is informed that the driver isactuating the resume or acceleration features of the cruise controlsystem.

Switch SW4 provides an input signal to IN5 of ECM 20 indicative of theoperational state of the vehicle clutch. The vehicle clutch is activatedby clutch pedal 36. A mechanical linkage 38 interconnects switch SW4with pedal 36 so that switch SW4 is opened when the driver or operatordepresses clutch pedal 36 thereby mechanically disengaging the engine ofthe vehicle from the transmission of the vehicle. Switch SW4 is normallyclosed, thus when the clutch pedal 36 is released, a +V_(DC) signal issupplied to input IN5 of ECM 20. When switch SW4 is opened, as a resultof clutch pedal 36 being depressed, switch SW4 opens and resistor R4pulls the input IN5 to logic low or ground.

Switch SW5 is a driver-operated switch which provides an input signal tothe ECM 20 regarding the operating state (on/off) of the enginecompression brake desired by the driver. Switch SW5 is a normally openswitch which, when closed, supplies a high logic signal level to inputIN7 of ECM 20 indicating engine brake operation is desired. When switchSW5 is open, resistor R7 pulls input IN7 to logic low or ground, therebyproviding ECM 20 with a logic low signal corresponding to a driverrequest to disable or discontinue engine brake operation.

Accelerator pedal 40 is mechanically coupled, via linkage 42 to thewiper W1 of potentiometer P1. The wiper W1 is connected to an analog todigital (A/D) converter input A/D1 of ECM 20. The position ofaccelerator pedal 40 corresponds directly to the voltage present onwiper W1. Since potentiometer P1 is connected at one terminal to +V_(DC)and at the other terminal to ground, the voltage present on wiper W1ranges from ground to +V_(DC). In this application, when acceleratorpedal 40 is in the throttle closed or non-depressed position, thevoltage present on wiper W1 is below a predetermined voltagecorresponding to a throttle closed position. If the wiper W1 voltage isabove a predetermined voltage, it is considered by the ECM 20 to be anindicator that the throttle is open.

Output OUT1 of ECM 20 supplies a signal to engine compression brake 24which is a part of the engine of the vehicle (not shown), to provideengine compression braking operation as is well known in the operationof heavy duty trucks. Output OUT2 of ECM 20 provides continuouslyvariable signals which control the fuel supply controller 26. Thecontinuously variable signals supplied to fuel supply controller 26enables ECM 20 to fuel the engine of the vehicle to any particular rpm(revolutions per minute) desired. Fuel supply controller may take theform of a fuel shut-off valve, fuel injectors or other fuelingmechanisms responsive to electronic signals for controlling fuel supplyrates to an engine.

The manual automatic transmission 28 is connected via various signalpath lines to ECM 20. Two different embodiments of particulartransmission I/O interfaces are shown in FIGS. 2 and 3. Speed sensor 30and RPM sensor 22 supply signals to ECM 20 indicative of the vehiclespeed and engine speed, respectively. RPM sensor 22 supplies a pulsetrain signal to input IN6 of ECM 20. The pulse train signal supplied toinput IN6 is monitored by ECM 20 to determine engine RPM speed.Similarly, the speed sensor 30, which detects tail shaft or drive shaftrotational speed, provides a similar pulse train signal to input IN8 ofECM 20 wherein the frequency of the pulse train delivered to ECM 20indicates the speed of rotation of the output shaft of the transmission28 or the drive shaft of the vehicle drive train.

The interface between ECM 20 and manual/automatic transmission 28, orMAT 28, is more specifically shown for two different transmissions inFIGS. 2 and 3. The I/O interface between ECM 20 and manual/automatictransmission 52 shown in FIG. 2 includes a gear position logic feedbacksignal supplied to input IN10 as well as an automatic shift-mode requestswitch SW6 that supplies a logic signal to input IN11 indicating whetherautomatic gear shifting operation is desired. Switch SW6 is actuated inresponse to driver positioning of gearshift lever 50. Gear shift lever50 is coupled to switch SW6 via actuator linkage 54. Resistor R6maintains the logic signal present at input IN11 of ECM 20 at a logichigh whenever normally open switch SW6 is not closed. When switch SW6 isclosed, the logic signal present at input IN11 is at a logic low level.Logic signals supplied to outputs OUT3 and OUT4 of ECM 20 control theactuation of sixth gear and seventh gear solenoid actuators (not shown)of the MAT 52. MAT 52 is a Spicer transmission Model No. AS125-7manufactured by Spicer, a subsidiary of Dana Corporation. The signalsupplied from MAT 52 to input IN10 of ECM 20 is a logic signalindicating that MAT 52 is in a neutral (no gears engaged) operationalstate when the signal is at a logic low level. When the signal suppliedto input IN10 of ECM 20 from MAT 52 is a logic high signal, an "in-gear"state of operation of MAT 52 is indicated. The signal supplied to inputIN10 does not indicate which automatically selectable gear ratiooperation state is currently engaged. Nevertheless, ECM 20 is aware ofthe logic output levels at outputs OUT3 and OUT4. Thus, ECM 20 candetermine whether MAT 52 has been placed into sixth gear automaticoperation state or seventh gear automatic operation state by the statusof outputs OUT3 and OUT4. Switch SW6 is actuated only when shift lever50 is placed into the automatic operation mode position depicted by theshift position A in FIG. 4 wherein automatic actuation of sixth andseventh gear is requested by the driver of the vehicle. The other shiftlever positions of FIG. 4 correspond to the reverse, first, second,third, fourth, and fifth gear ratio operation states which are manuallyselectable or engageable by the driver.

In an alternative embodiment of the present invention shown in FIG. 3,ECM 20 is electronically connected to and interfaced with MAT 70, anEaton/Fuller, Inc. transmission model RTT 12609A. The only I/O interfacesignal required between MAT 70 and ECM 20 is an output signal fromoutput OUT3 supplied to the splitter gear box electro-pneumatic solenoidactuator (not shown) of MAT 70. The splitter gear box of MAT 70 providesan overdrive gear ratio when the MAT 70 is in the highest speed gearoperation state. This is further illustrated in FIG. 5 by the gearshiftpattern shown which corresponds to the Eaton/Fuller MAT 70. Neutral isfound at position 90. Reverse gears are selectable at position 92 andforward gear ratio operational states that are manually selectable areshown at positions 94, 96, 98, 100, and 102. Once the driver has shiftedmanually through the gears according to the shift order of low, one,two, three, four, five, six, seven, and finally shifted the MAT 70 intothe manual gearshift position labeled 8/A, the automatic shiftingfunction of the ECM software is activated to shift back and forthbetween high split and low split to provide an overdrive final driveratio or higher speed capability gear ratio for MAT 70. Thus, atlocation 102 the position labeled 8/A is the last manually selected gearposition during the manual gear shifting phase of vehicle operationprior to the engagement or selection of automatic shift-mode operation.Subsequently, gear shifting occurs in the "top two" gears according toshift algorithms contained within ECM 20.

The Eaton/Fuller embodiment of the present invention does not requireswitch SW6 since the auto-shift mode is detected, through software, bycomparing engine speed and tailshaft speed. If the ratio of engine speedto tailshaft speed is within a predetermined ratio range, ECM 20recognizes that the driver has shifted MAT 70 into position 102 in FIG.5, Thereafter, until the ratio of engine speed to tailshaft speed fallsoutside the predetermined ratio range, ECM 20 controls the "top two"gears of MAT 20 according to shift algorithms forming a part of the ECM20 software.

Although the interface between MAT 52 and ECM 20 versus the interfacebetween MAT 70 and ECM 20 are substantially different, the operationalfeatures are significantly similar when either MAT 52 or 70 is placedinto the automatic shift-mode operation state wherein the "top two"final drive gear ratio operation states are automatically selected bythe ECM 20. Two electro-pneumatic solenoid valves (not shown) areactuated by logic signals supplied to output OUT3 and output OUT4 of ECM20 in FIG. 2 to engage sixth gear, seventh gear or neutral operationmode of MAT 52. Pressurized air and air cylinder(s) (not shown) withinthe MAT 52 or 70 supply the automatic shift mode gear engaging actionaccording to the position of the solenoid valve(s).

One electro-pneumatic solenoid valve is required to operate the splitterof MAT 70 shown in FIG. 3. Thus, the signal supplied to output OUT3actuates an electro-pneumatic solenoid valve (not shown) which actuatesthe splitter of MAT 70. The embodiments shown in FIG. 2 and FIG. 3 bothinclude power and ground signals supplied via signal path 58 between theECM 20 and the MATs 52 and 70.

Operationally speaking, the sequence of events which takes place when anauto-shift is to be performed in the top two gears of the system shownin FIG. 1 and FIG. 2 or FIG. 3 includes the following sequence of events(and is reflected in the flowchart of FIG. 7): (1) confirm that one ofthe top two gears is engaged, (step 700), (2) determine if an auto-shiftis necessary, (step 702), (3) disable cruise control and engine brakesif active, (step 704), (4) command the transmission shift solenoid (orsolenoids) to the requested gear, (step 706), (5) fuel the engine toproduce a torque reversal in the transmission and drive train, (step708), (6) confirm disengagement of the current gear, (step 710), (7)calculate synchronous engine speed to engage desired auto-shift gearratio operation state, (step 712), (8) fuel engine to achievesynchronous engine speed, (step 714), (9) confirm gear engagement, (step716), (10) ramp the engine torque available to the driver, (step 716),(11) return engine brakes and cruise control to their operational stateprior to the auto-shift sequence initiation, (step 718), and (12) delaya fixed period of time before attempting another auto-shift (step 720).

A number of operational factors or conditions are monitored to determinewhether to initiate or inhibit an auto-shift sequence. The ECM 20continuously monitors the system inputs numerous times a second todetermine whether or not an auto-shift sequence can be initiated. Apreferred repetition time span is approximately 96 milliseconds,although other repetition time intervals are contemplated; that is theECM 20 should determine whether an auto-shift condition is present andwhether an auto-shift should be initiated every 96 milliseconds. Anauto-shift is inhibited if any of the following conditions exist: (1)one of the top gears is not confirmed as engaged, which is a conditionprecedent for an automatic mode upshift or an automatic mode downshift,(2) vehicle speed is below a predetermined level, (3) the clutch pedalis depressed before or during the auto-shift process, (4) a shift delayhas not elapsed since the previous auto-shift, and (5) other systemfaults which indicate to the ECM 20 that an automatic mode shift orauto-shift should not occur, such as speed sensor or RPM sensor failure,or other such hardware failures which prevent proper and safe operationof the auto-shift mode of operation.

In addition to determining when an auto-shift should occur, the controlsystem of FIG. 1 also provides cruise control mode operation of thevehicle in conjunction with the auto-shift control of MAT 28. Thecontrol logic of ECM 20 will initiate automatic upshifts, shifting froma lower to a higher vehicle speed gear ratio operation state, in"non-cruise" mode when the engine speed approaches the rated enginespeed for the engine. Automatic "non-cruise" downshifts will beinitiated when the engine speed is below a percentage of the"non-cruise" upshift engine speed to introduce hysteresis and preventgear-hunting or constant gear shifting when the engine is fueled to movethe vehicle at a speed close to or at a speed corresponding to anauto-shift shift point speed. Control logic or software within ECM 20executes an automatic downshift in "non-cruise" mode when the throttlepedal is in the idle position (throttle closed) and when the enginespeed falls below a minimum predetermined speed, typically (0.68) *(High₋₋ Idle). High₋₋ Idle is defined as 1700-1800 RPM, which value isthe maximum engine RPM before an electronic road speed governor(included in the software of ECM 20) decreases fueling to preventfurther increases in engine RPM.

In addition, the control logic of ECM 20 determines the engine RPM speedat which automatic upshifts and downshifts will occur while in the"cruise" mode based upon an algorithm which provides variable shiftpoints in response to operating conditions sensed by ECM 20. ECM 20controls exclusively the engine brakes, clutch operation, and enginefueling during the auto-shift period.

Equipment failures which may result in undesirable operation of thevehicle must be anticipated and properly handled when they occur. Anundesirable equipment failure state occurs when the switch SW6 of FIG. 2fails "open" or fails "closed". For example, if the switch SW6 fails toopen properly, the auto-shift mode is never enabled. This presents aproblem since the transmission remains in neutral after the driver hasrequested auto-shift operation. If by chance the vehicle is travelingdownhill at the time, the transmission is not placed into gear and thedriver must use the service brakes to slow the vehicle. On the otherhand, if switch SW6 fails in the "closed" state, the control system 15is instructed or tricked into selecting one of the top two gears at alltimes. If the vehicle should slow down or come to a stop or encounter anincline, lower gear selection is impossible, therefore the vehicle maystall due to improper gear selection. Another undesirable condition canexist due to the driver intentionally allowing the vehicle to coastdownhill in a neutral state to achieve higher speeds than the road speedgovernor would normally allow, (i.e. in excess of the rated speed of theengine). Thus, several algorithms must be included in the software ofthe ECM 20 in order to compensate for equipment failure modes andprovide desirable operation of the control system 15 of FIG. 1.

During normal operation of the control system 15 in conjunction with theMAT 52 of FIG. 2, the driver at some time will request auto-shift modeby moving the shift lever 50 to the top gear position shown in FIG. 4 asshift position A of the shift pattern 80. By doing so, the driver hasclosed switch SW6 and the control system 15 automatically controlsshifting of the MAT 52 "top two" gears as long as operating conditionsdictate normal auto-shift operation of these two gears. During vehicleoperation with the shift lever 50 in a position other than the top gearposition, or the A shift position of FIG. 4, control system 15 iscontinuously monitoring vehicle operating conditions. If operatingconditions are detected which indicate the vehicle transmission shouldbe in one of the "top two" gears, which conditions are mutuallyexclusive with operating conditions in any lower gear, signals aresupplied to outputs OUT3 or OUT4 by ECM 20 to shift the transmissioninto the lowest of the top two gears that can be achieved under theoperating conditions present at the time of the command. Some operatingconditions that are monitored include: (1) whether the MAT 52 is inneutral as indicated by the feedback signals supplied to inputs IN9 andIN10 of ECM 20 or, with respect to MAT 70, that the gear ratiocomputations derived from the RPM sensor 22 and speed sensor 30 inputscorrespond to an unknown gear ratio operating state for MAT 70 or aneutral state of operation, and (2) the present vehicle speed.

Two separate control algorithms are continuously executed by ECM 20 thatmonitor operating conditions and control MAT 52 or MAT 70 to preventundesirable operating conditions. Referring now to FIG. 8, the firstalgorithm is depicted. At step 802, a timer loop is implemented so thatthe remainder of the algorithm in FIG. 8 is executed by ECM 20 every 96milliseconds. After the expiration of 96 milliseconds, program executioncontinues at step 804 and ECM 20 tests whether the vehicle speed isbelow a predetermined low speed limit. Below a specified speed such as 5MPH, the MAT should not be in one of the top two gears. If the vehiclespeed is above the low speed limit, program control returns to step 802.If the vehicle speed is detected as below the predetermined low speedlimit in step 804, then it is next necessary to test whether the vehicleis "skidding", i.e., the driver has applied the brakes excessively andthe vehicle wheels are not rotating before any automatic gear shiftevents may occur. A suggested low speed limit for use in step 804 isfive (5) miles per hour. A "vehicle skidding" test is performed at step806 to determine how ECM 20 will respond to the current operatingconditions sensed. If the vehicle is skidding, a predetermined timedelay must pass before ECM 20 tests whether an autoshift of the top twogears is in progress at step 807. If an autoshift is in progress thenprogram execution continues at step 816 after step 807. If an autoshiftis not in progress at step 807, then step 808 is next executed. At step808 the vehicle speed is sensed by ECM 20. If the speed of the vehicleis below 5 MPH step 810, then the MAT is commanded to a neutral statevia appropriate setting of the OUT3 and OUT4 outputs in step 812. If thesensed vehicle speed at step 810 is above a low speed (such as 5 MPH),then the MAT is not shifted to neutral and program execution returns tostep 802. Fuel control of the engine is unaffected in step 812. Afterstep 812 program execution returns to step 802.

If it is determined at step 806 that the vehicle is not skidding, thenstep 814 follows step 806, and ECM 20 determines whether an autoshift iscurrently in progress. If an autoshift is occurring, then the autoshiftsequence is allowed to continue at step 816. If an autoshift sequence isnot in progress at step 814, then the state of MAT 52 is detected atstep 818. If MAT 52 is already in a neutral state, then programexecution continues at step 802 following step 818. If MAT 52 is not ina neutral state at step 818, then MAT 52 is commanded to neutral by ECM20 via control of outputs OUT3 and OUT4 at step 820. Program executioncontinues at step 802 after steps 816 and 820.

A second algorithm shown in FIG. 9 addresses an excessive vehicle speedcondition to control MAT 52 and prevent an undesirable state ofoperation. Referring to FIG. 9, the algorithm is executed every 96milliseconds by way of the time expired test of step 902. If 96milliseconds has expired, as tested at step 902, then the state of MAT52 is detected through input signal IN10 by ECM 20. If sixth or seventhgear is engaged at step 904 then no action is required and programexecution continues at step 902. If neither 6th or 7th gear is engagedat step 904, then the vehicle speed is sensed by ECM 20 at step 906. Ifthe vehicle speed is greater than a maximum limit vehicle speed thenprogram execution continues at step 908. At step 908, ECM 20 checks forvarious system faults, and if none is detected, then MAT 52 is commandedinto 7th gear without taking fuel control from the driver at step 910.Program execution continues at step 902 following step 910. If vehiclespeed is below the maximum limit at step 906, then program executioncontinues with step 902. The control algorithm of FIG. 9 ensures thatMAT 52 is in 7th gear if the vehicle speed is excessive, e.g., greaterthan 65-70 MPH, thus preventing out-of-gear coasting at high speeds.

During the normal downshift process for the auto-shift mode of operationof the system 15, switch SW5 provides an input to ECM 20 indicatingwhether engine compression brake operation is desired during braking ordeceleration of the vehicle. Switch SW5 is located in the cab area ofthe heavy duty truck and is a mechanical switch operable by the driverof the vehicle. Normally, the engine brakes 24 are active or enabledwhen the switch SW5 is positioned accordingly, throttle is not appliedor closed, and the clutch is engaged (pedal 36 out). If the driver hasselected engine brake operation, and shifts the transmission in neutraland releases the throttle and clutch pedal, the engine brake willdisengage below a predetermined engine RPM. This is an undesirablecondition or result. In addition, during an electronically controlledshift, the clutch pedal 36 must be out and the engine speedelectronically controlled for the auto-shifting process. This conditionor set of conditions contradicts normal engine brake logic. Morespecifically, if the auto-shift gear requested fails to engage, with theengine compression brakes engaged, the engine brake must disengage belowa predetermined RPM to prevent the engine from stalling. For anelectronically controlled auto-shift to be performed correctly, completeengine control must be maintained by the control system 15. If theengine compression brakes are engaged and conditions are sensed whichallow or enable the control system to perform an electronicallycontrolled downshift, the ECM 20 must have enabling/disabling control ofthe engine compression brakes so that the engine can be allowed toaccelerate to achieve synchronous RPM to allow gear engagement. Thecontrol system 15 is able to achieve synchronous RPM for the engine viaa control signal supplied to fuel supply controller 26 at output OUT2.Another possible operating condition that can damage the engine occursif the engine is fueled during compression brake operation. This canresult in severe engine damage, and may occur in the case when anelectronically controlled auto-shift mode downshift occurs and fuelsupply controller 26 is unable to raise the engine RPM to synchronousRPM speeds required for the gear shifting operation.

Thus, in order for the control system 15 to provide for safe operationof an engine compression brake 24, the above undesirable conditions foroperation of the engine compression brake 24 must be detected and enginecompression brake operation disabled during the time periods whereinengine brake operation is undesirable.

ECM 20 monitors the condition of the auto-shift sequence, current gearratio (determined by the ratio of the input signals received from theRPM sensor and the vehicle speed sensor) the signal from the enginebrake switch SW5, the signal from the clutch switch SW4, and theposition of the throttle as indicated by the voltage present on wiper W1supplied to A/D1 input of ECM 20 to determine whether an engine brakeenable signal is supplied to output OUT1 thereby enabling operation ofengine compression brake 24. By using the above inputs to ECM 20 ascomponents of a logic equation, an algorithm is implemented toenable/disable engine compression brake operation. The logic algorithmis as follows: if wiper W1 voltage is less than a predetermined throttleclosed voltage and switch SW4 is closed and switch SW5 is closed and thefinal drive gear ratio is verified as a valid gear ratio (as determinedusing the input signals from speed sensor 30 and RPM sensor 22) and ECM20 is not currently undertaking to execute an auto-shift operation thenactivate the compression brake 24 via a signal supplied at output OUT1.If all of the separate conditions in the equation are true then thecompression brakes are activated. Without this algorithm for controllingcompression brake operation, there is no guarantee that the vehicle is"in gear", the basic requirement for desirable and correct operation ofthe compression brake. The means to ensure that proper conditions existbefore activating the compression brake is reliant upon the abovedetected logic conditions. In order to accomplish electronicallycontrolled automated gear ratio shifts with a manual/automatictransmission and a compression brake installed on the engine, the aboveconditions must be verified prior to enabling or activating the enginecompression brake 24.

In addition to the previously described operational features of thecontrol system 15, another feature of the control system 15 according tothe present invention includes a means for providing variableelectronically controlled gear shift speed points for cruise andnon-cruise auto-shift operating modes. More specifically, softwareimplemented algorithms establish variable speed points at whichauto-shift mode gear shifts occur.

In a state or mode of operation wherein none of the cruise control modesare activated, the decisional algorithms for determining when anauto-shift upshift or downshift should occur are made in accordance withdetected vehicle speed, engine RPM speed and throttle position. Morespecifically, if cruise control is not active, then an auto-upshift willoccur if the engine speed is greater than the rated engine speed times afirst scaling factor with the throttle open or the engine speed isgreater than a second scaling factor times rated engine speed with thethrottle closed. This algorithm transforms into the following equation:

    __________________________________________________________________________    If       (RPM > NORMAL.sub.-- UP*HS.sub.-- IDLE.sub.-- RPM) .AND. (throttle =      open)! .OR.       (RPM > COAST.sub.-- UP*HS.sub.-- IDLE.sub.-- RPM) .AND. (throttle =      closed!    then upshift.    __________________________________________________________________________

wherein NORMAL₋₋ UP is a scaling factor, HS₋₋ IDLE₋₋ RPM is rated enginespeed, COAST₋₋ UP is a scaling factor, and RPM is actual engine speed.Values for NORMAL₋₋ UP and COAST₋₋ UP are typically 1.0 or less and areestablished in accordance with the engine torque curve, the transmissiongear ratios for the top two gears and the final drive ratio of thevehicle drivetrain. A typical value for NORMAL₋₋ UP is approximately 1.0and a typical value for COAST₋₋ UP is approximately 1.0. Increasedflexibility is provided by setting COAST₋₋ UP to a value different fromNORMAL₋₋ UP thereby forcing an upshift with throttle closed at a desiredengine rpm. Setting COAST₋₋ UP to a large value effectively disablesCOAST₋₋ UP from affecting shift speeds so that an upshift occurs only ifthe throttle is open and RPM is greater than NORMAL₋₋ UP times HS₋₋IDLE₋₋ RPM.

Accordingly, a non-cruise control downshift sequence is initiated by ECM20 in response to the detection of the following conditions: the enginespeed is less than or equal to a scaling factor (NORMAL₋₋ DWN) timesrated engine speed with the throttle open or the engine speed is lessthan or equal to a scaling factor (COAST₋₋ DWN) times rated engine speedwith the throttle closed. This logical algorithm transforms into thefollowing equation:

    __________________________________________________________________________    IF       (RPM <= NORMAL.sub.-- DWN*HS.sub.-- IDLE.sub.-- RPM) .AND. (throttle =      open)!      .OR.       (RPM <= COAST.sub.-- DWN*HS.sub.-- IDLE.sub.-- RPM) .AND. (throttle =      closed)!    then downshift.    __________________________________________________________________________

wherein NORMAL₋₋ DWN * HS₋₋ IDLE₋₋ RPM is an engine speed below ratedengine speed, and COAST₋₋ DWN * HS₋₋ IDLE₋₋ RPM is an engine speed belowrated engine speed and below NORMAL₋₋ DWN * HS₋₋ IDLE₋₋ RPM. NORMAL₋₋DWN and COAST₋₋ DWN are scaling factors that enable tailoring thedownshift speeds to a specific driveline combination in view of ratedengine speed, transmission gear ratios and final drive gear ratios ofthe vehicle. COAST₋₋ DOWN can be set above or below NORMAL₋₋ DOWN but isnormally below or equal. Setting COAST₋₋ DWN to a very small scalingfactor prevents a downshift attributable to an engine speed less than(COAST₋₋ DWN * HS₋₋ IDLE₋₋ RPM).

Typical values for the above are HS₋₋ IDLE₋₋ RPM=1800, (NORMAL₋₋ DWN *HS₋₋ IDLE₋₋ RPM)=1300, (COAST₋₋ DWN * HS₋₋ IDLE₋₋ RPM)=1100, (NORMAL₋₋UP * HS₋₋ IDLE₋₋ RPM)=1650 and (COAST₋₋ UP * HS₋₋ IDLE₋₋ RPM)=1750.

Closed throttle is detected when the throttle or accelerator pedal 40positions wiper W1 of FIG. 1 so that the voltage supplied to input A/D1is below a predetermined voltage. Open throttle is detected when the ECM20 detects a voltage on wiper W1 greater than the voltage correspondingto a closed throttle condition.

In the case of variable speed shift points during cruise controloperation of the control system 15, a review of basic cruise controlsystem functional operation is essential to a proper systemunderstanding. The cruise control system incorporated into the controlsystem 15 responds to actuation of switches SW2 and SW1. Fuel supplycontroller 26, clutch 27 and manual/automatic transmission 28 arecontrolled by ECM 20 in response to detection of certain operatingcondition parameters at the inputs of ECM 20. Cruise control switch SW2enables cruise control mode of operation when closed. When cruisecontrol is enabled, several modes of operation are available including a"set" mode, a "coast" mode, a "resume" mode, and an "acceleration" mode.These modes are typical operating modes found in contemporary cruisecontrol systems for motor vehicles and are well known in the art ofcruise control systems. In the "set" mode of operation, switch SW1 isactivated so that a high logic level signal is supplied to input IN3 ofECM 20. By requesting "set" mode, the driver has indicated that theparticular speed which is sensed via speed sensor 30 at input IN8 of ECM20, is the desired or cruise speed at which the driver wishes thevehicle to continue to operate at or "cruise". Switch SW1 has aspring-return-to-center operation between the center off position andthe set/coast position. Thus, the operator or driver must physicallymove the switch to the set/coast position in order to achieve the set orcoast mode of operation. Upon the first closure of switch SW1 againstthe set/coast contact, ECM 20 maintains the speed signal sensed at inputIN8 by controlling fuel supply controller 26 and the manual/automatictransmission 28. Upon the operator depressing the brake pedal 32, switchSW3 is closed momentarily, and a high level logic signal supplied toinput IN1 of ECM 20 will deactivate the cruise control "set" mode ofoperation, and the ECM 20 releases its control of fuel to the engine viafuel supply controller 26 and returns throttle control to the driver.However, the control of auto-shifting operations by ECM 20 does notcease with the activation of brake switch SW3 until the driver of thevehicle actively disables the auto-shift operation state by moving theshift lever out of the auto-shift mode position, or vehicle speed dropsbelow a predetermined limit such as 20 miles per hour.

If a desired set speed has been input using switch SW1 and the ECM 20 isattempting to maintain a constant vehicle speed or "cruise", and thedriver subsequently closes switch SW1 again into the "set/coast"position, the system 15 returns throttle control to the driver and thedesired "set" speed is replaced by the vehicle speed detected when thedriver subsequently releases switch SW1 from the position wherein a highlogic level signal is supplied to input IN3 of ECM 20. Thus, in the"coast" mode, the driver may increase or decrease the cruise speed byactivating the coast mode (closing SW1 to set/coast position) toestablish a new cruise speed for the vehicle.

When switch SW1 is toggled from the center off position to theresume/accel position, thereby supplying a high level logic signal toinput IN4 of ECM 20, one of two other possible modes is activated. If adesired cruise speed has been previously established and the ECM 20 hasreceived signals indicating that the ignition switch (not shown) has notbeen turned off, then the ECM 20 will maintain the previously set cruisespeed in memory regardless of the condition of the brake pedal 32 andthe brake switch SW3. However, ECM 20 releases control of the fuelsupply controller 26 and allows the driver of the vehicle to control thefueling rate of the engine in this operating mode with cruise on, i.e.switch SW2 closed, and the brake pedal depression having deactivated thecruise mode. When the driver activates switch SW1 so that a logic highis supplied to input IN4, or to the "resume/accel" position, ECM 20 willagain take over control of supplying fuel to the engine and via a signalsupplied to output OUT2 attempt to change the speed of the engine toresume the desired or requested vehicle "set" speed. If during "set"mode cruise control operating conditions the driver wishes to increasethe cruise control "set" speed or accelerate, the driver need only moveswitch SW1 to the "resume/accel" position, thereby supplying a highlogic level signal to input IN4 of ECM 20, to indicate to ECM 20 that anincreasingly higher cruise "set" speed is desired. By holding the switchin this position, the driver can increase the speed of the engine andvehicle and then release switch SW1 so that it spring returns to thecenter off position. The vehicle speed sensed when switch SW1 isreleased to the center off position will be the new "set" speed forcruise control operation.

In addition to fueling the engine to maintain a constant vehicle speedduring cruise control operation, the ECM 20 must also determine when toshift the "top two" gears of MAT 28 in order to achieve maximum fueleconomy as well as desired operational shifting characteristics. Thefollowing logical equations are used to determine the variable shiftpoints for upshift and downshift conditions of the top "two gears" ofMAT 28 during cruise control operation of system 15:

    ______________________________________    If   (RPM < CRUISE.sub.-- DWN.sub.-- RPM*HS.sub.-- IDLE.sub.-- RPM)        .AND.        (CRUISE.sub.-- SET.sub.-- SPEED-VSS > CRUISE.sub.-- DWN) .OR.        (RPM < CRU.sub.-- DWN.sub.-- RPM2*HS.sub.-- IDLE.sub.-- RPM)!    then downshift,    If   (RPM > CRUISE.sub.-- UP.sub.-- RPM*HS.sub.-- IDLE.sub.-- RPM) .AND.        (CRUISE.sub.-- SET.sub.-- SPEED-VSS < CRUISE.sub.-- UP) .OR.        (RPM > CRU.sub.-- UP.sub.-- RPM2*HS.sub.-- IDLE.sub.-- RPM)!    then upshift.    ______________________________________

The downshift equation in cruise control mode with accel mode, coastmode or throttle override mode active is:

    ______________________________________    If  RPM < NORMAL.sub.-- DWN*HS.sub.-- IDLE.sub.-- RPM (rated engine        speed)    then downshift;    ______________________________________

and the upshift equation in cruise control mode with accel mode, coastmode, or throttle override mode active is:

    ______________________________________    If  RPM > NORMAL.sub.-- UP*HS.sub.-- IDLE.sub.-- RPM (rated engine        speed)    then upshift.    ______________________________________

Several values in the above equations are defined in terms of ratedengine speed or HS₋₋ IDLE₋₋ RPM multiplied times a scaling factor.NORMAL₋₋ DWN is a scaling factor multiplied times HS₋₋ IDLE₋₋ RPM toobtain the engine speed at which an automatic downshift from the topgear takes place. NORMAL₋₋ UP is a scaling factor multiplied times HS₋₋IDLE₋₋ RPM to ascertain the engine speed at which an automatic upshiftinto the top gear takes place. The engine torque curve, transmissiongear ratios for the top two gears and final drive ratio of the vehicledriveline are factors directly affecting the selection of values forNORMAL₋₋ UP and NORMAL₋₋ DWN. Selecting appropriate values for NORMAL₋₋DWN and NORMAL₋₋ UP in conjunction with the final drive ratio of atransmission and the differential drive ratio of the vehicle provides aneffective technique to utilize an engine control system with a varietyof engine/transmission/drivetrain combinations by varying but a fewparameters supplied to the ECM 20. Typically, NORMAL₋₋ UP and NORMAL₋₋DWN are values less than 1.0. For example, if the peak torque of anengine is 1300 and HS₋₋ IDLE₋₋ RPM is 1800 then NORMAL₋₋ UP is set to1.0 so that an upshift to the top gear will occur at HS₋₋ IDLE₋₋ RPM or1800 RPM, and vehicle acceleration in the top gear of the transmissionoccurs in the peak area of the engine's torque curve. Similarly, as thevehicle decelerates and RPM falls, a downshift in the top two gearsbecomes necessary when engine RPM falls below a predetermined limit. Thelower RPM limit at which a downshift occurs is controlled by NORMAL₋₋DWN as a function of HS₋₋ IDLE₋₋ RPM. For example, if HS₋₋ IDLE₋₋ RPM is1800 and NORMAL₋₋ DWN is 0.72, then at (0.72*1800) RPM (or 1296 RPM) adownshift is determined necessary, and ECM 20 carries out the downshiftvia the previously described auto-shift sequence.

Other variables in the above shift equations are defined as follows:

(a) CRUISE₋₋ SET₋₋ SPEED is the set speed for cruise control;

(b) CRUISE₋₋ DWN₋₋ RPM is a scaling factor used to calculate an RPMvalue below and within a predetermined range of rated engine speed ofthe engine, a typical value for CRUISE₋₋ DWN₋₋ RPM is 0.68;

(c) VSS is current vehicle speed;

(d) CRU₋₋ DWN₋₋ RPM2 is a scaling factor used to calculate apredetermined engine speed value less than CRUISE₋₋ DWN₋₋ RPM, a typicalvalue for CRU₋₋ DWN₋₋ RPM2 is 0.62;

(e) CRUISE₋₋ UP₋₋ RPM is a scaling factor used to calculate apredetermined engine speed value within a predetermined range of therated engine speed, a typical value for CRUISE₋₋ UP₋₋ RPM is 0.89;

(f) CRU₋₋ UP₋₋ RPM2 is a scaling factor used to calculate apredetermined engine speed value less than CRUISE₋₋ UP₋₋ RPM, a typicalvalue for CRU₋₋ UP₋₋ RPM2 is 1.0;

(g) CRUISE₋₋ DWN is a predetermined vehicle speed value subtracted fromCRUISE₋₋ SET₋₋ SPEED to determine the speed at which a downshift isrequested, a typical value for CRUISE₋₋ DWN is 4 mph;

(h) CRUISE₋₋ UP is a predetermined vehicle speed value added to CRUISE₋₋SET₋₋ SPEED to define the vehicle speed at which an upshift isrequested, a typical value for CRUISE₋₋ UP is 2 mph.

Throttle override occurs when the driver depresses the accelerator pedalwhile cruise control mode is active to increase vehicle speed above thecruise₋₋ set₋₋ speed or to increase acceleration of the vehicle abovethe acceleration rate set by ECM 20 to attain cruise₋₋ set₋₋ speed.

Auto-shift algorithms for determining when an upshift or downshiftshould occur between the "top two" gears of MAT 28 provide enhancedoperation of the manual/automatic transmission system and a moresophisticated cruise control system for heavy duty truck vehicles. Theheavy duty truck in which the system 15 is installed includes a CumminsN14 or L10 engine equipped with a CELECT electronic engine controlmanufactured by Cummins Electronics Incorporated, a subsidiary ofCummins Engine Company, Inc., of Columbus, Ind. The software included inthe CELECT (shown in FIGS. 6 and 6A) engine control module or electroniccontrol module is modified and additional hardware is added to controlthe Eaton or Spicer transmissions. The Eaton transmission is a modelRTT-12609A splitter-type transmission and the Dana Spicer transmissionis a model AS125-7 rail-type transmission. With either Cummins-Eaton orthe Cummins-Spicer drive-line configuration, the additional softwareresident in the CELECT ECM will monitor the vehicle's performance andautomatically control the "top two" gears of the transmission in eithercruise or non-cruise operating modes. The variable speed shift pointalgorithms are designed to optimize gear shift points and maximum fueleconomy without any loss in driveability of the vehicle.

The software executed by the CELECT system is included in thisapplication and can be found following the Description of the PreferredEmbodiment. The software is written in assembly language and wasdeveloped using an Apollo development system and is executable by aModel 80196 Intel microcomputer.

Referring now to FIG. 6, a diagrammatic illustration of an electroniccontrol system 200 according to the present invention is shown whichincludes all of the components of system 15 of FIG. I and additionalsystem capability. The principal components of this system are ECM 206,engine 202, cab mounted hardware within cab area 204 and transmission280. ECM 206 corresponds with ECM 20 of FIG. 1. Three wiring harnessesare connected to ECM 206 at locations A, B and C. At location A, asensor harness 300 is connected to ECM 206. Sensor harness 300 providessignal paths for connecting sensors to ECM 206. OEM harness 302 providesconnections between cab area mounted hardware, the vehicle speed sensor290 of transmission 280 and ECM 206. Actuator harness 304 connected tolocation C of ECM 206 provides signal paths for actuation of the variousdevices hereinafter described which control the operation of thetransmission and engine. In addition, a signal from ignition key switch230 is supplied to an input of ECM 206 via harness 304.

The switches, lamps, and other devices mounted in the truck cab area 204provide the driver with means for controlling the system functions aswell as feedback in the form of lamps, LED's and displays which indicatesystem status. Clutch switch 212, brake switch 214 and cruise controlswitches 236 correspond to the clutch switch SW4, brake switch SW3 andcruise control switches SW1 and SW2 of FIG. 1, respectively. Enginebrake on/off switch 216 corresponds to switch SW5 of FIG. 1. Acceleratorposition sensor assembly 220 corresponds to potentiometer P1 of FIG. 1.Tachometer 224 provides the driver with visual feedback regarding enginespeed or RPM. Battery 226 supplies electrical power to the systemthrough fuse 228. Vehicle key switch 230 is connected to engine brakerelay unit 242 and to ECM 206. Fault lamps 232 provide the driver withfault indications regarding system operation. Engine protection faultlamps 234 provide driver feedback regarding faults associated withoperation of engine 202. Switch 238 is a center-off single-poledouble-throw switch which, when activated, provides increment anddecrement input signals to ECM 206 associated with an idle/diagnosticsmode. Switch 240 provides an input to ECM 206 indicating that theoperator wishes to enter the diagnostic test mode. Data link 241 isprovided so that additional electronic hardware can be connected to theOEM harness 302 to communicate with ECM 206 and retrieve data stored inECM 206 regarding operating history and faults experienced by ECM 206over a period of time during which the software within ECM 206 hasexecuted and monitored the operational parameters of the system 200.

Engine brake relay unit 242 receives a power signal from vehicle keyswitch 230 and provides signals to cylinder selection device 244 forcontrol of the engine brake unit 208. Pairs of engine cylinders areindividually controlled by brake controller devices 246, 248 and 250, sothat engine braking action can be actuated in a three-stage fashion toprovide three different levels of engine braking action. Engine brake208 is well known in the art of heavy-duty engines and is sold byCummins Engine Company, Inc. of Columbus, Ind.

Engine 202 includes cylinder block 260 wherein fuel injectors 258 aremounted. Fuel injectors 258 are controlled by signals from ECM 206. Fuelshut-off valve 254 and waste gate solenoid 256 are directly controlledby ECM 206. Fan clutch solenoid 252 is activated by ECM 206 according tooperating conditions dictated by the software of 206. Coolant levelsensor 262, oil pressure sensor 264, oil temperature sensor 266, engineposition sensor 268, boost pressure sensor 270, coolant temperaturesensor 272, ambient air pressure sensor 274 and intake manifoldtemperature sensor 276 provide input signals which enable monitoring ofoperating conditions and provide feedback signals regarding theoperating conditions of engine 202.

The embodiment of the devices shown in FIGS. 1 and 2 is more fully andcompletely shown by the diagrammatic illustration of FIG. 6. Thus, thetransmission 280 of FIG. 6 corresponds directly to the MAT 52 of FIG. 2.An input signal from top gear indicator 282 corresponds to the switchSW6 of FIG.. 2. Position feedback sensors 284 correspond to the neutralfeedback signal and in-gear feedback signals supplied to inputs IN9 andIN10 of FIG. 2, respectively. Shift solenoid 286 and shift solenoid 288are operated in response to signals supplied to output OUT3 and OUT4respectively of FIG. 2. Vehicle speed sensor 290 corresponds to thespeed sensor 30 of FIG. 1.

An embodiment comprising the system of FIG. 1 and FIG. 3 is illustratedessentially in FIG. 6 with the exception of transmission 280 beingreplaced by the transmission 281 of FIG. 6A. More specifically, theshift solenoid 287 of FIG. 6A corresponds to the device coupled tooutput OUT3 of ECM 20 in FIG. 3 and the vehicle speed sensor 290 oftransmission 281 corresponds to the speed sensor 30 of FIG. 1. Allremaining components are identical for the two systems. FIG. 6A depictsthe location of the shift solenoid and vehicle speed sensor of theembodiment shown in FIG. 3 thereby enabling one skilled in the art tounderstand more fully the componentry location of the control systemaccording to the present invention.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A device for controlling gearengagement/disengagement of a manual/automatic transmission which iscoupled to an engine, the transmission including a manual mode ofoperation wherein a plurality of gear ratio operation states areselectable according to a driver input and an automatic mode ofoperation wherein first and second automatically engagable gear ratiooperation states and a neutral operation state are selectable by saiddevice when the transmission is placed in the automatic mode ofoperation, said device comprising:shift means connected to thetransmission for selecting between manual mode and automatic mode ofoperation of the transmission; means for producing a top gear signalwhen said shift means is in the automatic mode of operation position;means for sensing vehicle speed and producing a speed signalcorresponding to vehicle speed; means for producing a skidding signal inresponse to an abrupt change in said speed signal; means for producing agear engagement signal in response to said top gear signal if said speedsignal is above a predetermined low speed limit and said skidding signalis not present; and means for engaging one of said first or secondautomatically engageable gear ratio operation states of saidtransmission in response to said gear engagement signal.
 2. The deviceof claim 1 including means for activating said neutral operation statein response to said speed signal indicating a vehicle speed below apredetermined low speed limit and when said means for engaging is notoperating to engage said first or said second automatically engagablegear ratio operation state.
 3. The device of claim 2 including:means forsensing engine speed and producing an RPM signal corresponding to enginespeed; means for producing a gear ratio signal corresponding to said RPMsignal divided by said speed signal; and wherein said means for engagingactuates the neutral operation state when said gear ratio signalcorresponds to either said first or said second automatically engagablegear ratio operation states and said speed signal is below saidpredetermined low speed limit, and wherein said means for engagingactuates said second automatically engagable gear ratio operation statewhen said speed signal is above a maximum speed limit, said secondautomatically engagable gear ratio state being the highest gear ratio ofsaid manual/automatic transmission.
 4. The device of claim 3 whereinsaid means for engaging includesa first solenoid actuator for operablyengaging the first gear ratio operation state of the transmission; asecond solenoid actuator for operably engaging the second gear ratiooperation state of the transmission; and means for fueling the engine toa synchronous RPM speed in response to said RPM signal wherein saidsynchronous RPM speed is mathematically determined from said speedsignal and from a final drive ratio of the transmission corresponding tosaid first or said second gear ratio operation state of thetransmission.
 5. The device of claim 4 wherein said means for producinga gear engagement signal and said means for fueling the engine arecomponents of an engine control module including a microcomputer,digital and analog I/O, ROM and RAM.
 6. A method for controlling gearengagement/disengagement of a manual/automatic transmission that iscoupled to an engine, wherein the transmission includes gear shiftmeans, a manual mode of operation wherein a plurality of gear ratiooperation states are selectable according to driver positioning of theshift means, said transmission also having an automatic mode ofoperation wherein first and second automatically engagable gear ratiooperation states and a neutral operation state are automaticallyselectable when the shift means are positioned in an automatic modeposition, said method comprising the steps of:producing a top gearsignal when said shift means is in the automatic mode position; sensingvehicle speed and producing a speed signal corresponding to vehiclespeed.; producing a skidding signal in response to an abrupt decrease insaid speed signal; producing a gear engagement signal in response tosaid top gear signal in combination with said speed signal being above apredetermined low speed limit and the absence of said skidding signal;and engaging one of said first or second gear ratio operation states ofsaid transmission in response to said gear engagement signal.
 7. Themethod of claim 6 wherein said first or said second gear ratio operationstates are engaged in response to the following conditions:a) inresponse to said top gear signal, and b) when said speed signal is abovesaid predetermined low speed limit.
 8. The method of claim 6 includingthe step of activating said neutral operation state in response to saidspeed signal falling below a predetermined low speed limit.
 9. Themethod of claim 8 including the steps of:sensing engine speed andproducing an RPM signal corresponding to engine speed; producing a gearratio signal corresponding to said RPM signal divided by said speedsignal; and engaging the neutral operation state when said gear ratiosignal is one of two predetermined gear ratio ranges and said speedsignal is below said predetermined low speed limit.
 10. The method ofclaim 9 wherein said engaging the neutral operation state step furtherrequires that said engaging one of said first or second gear ratiooperation states step is not taking place before said neutral operationstate is engaged.
 11. The method of claim 10 wherein said producing askidding signal step includes the steps of:detecting an abrupt decreasein said speed signal; monitoring said vehicle speed for a predeterminedtime period in the event vehicle skidding ends and said speed signalindicates the vehicle wheels are rotating; and producing said skiddingsignal if said speed signal still indicates an abrupt decrease invehicle speed. .Iadd.12. A device for controlling gearengagement/disengagement of a manual/automatic transmission which iscoupled to an engine, the transmission including a manual mode ofoperation having a plurality of manually selectable gear ratio operationstates and an automatic mode of operation having first and secondautomatically engageable gear ratio operation states selectable by saiddevice, said device comprising: shift means connected to thetransmission for selecting between manual mode and automatic mode ofoperation of the transmission; means for sensing vehicle speed andproducing a vehicle speed signal corresponding thereto; means forproducing a skidding signal in response to an abrupt change in saidvehicle speed signal; means for producing a gear engagement signal whenthe shift means is in the automatic mode of operation if said vehiclespeed signal is above a predetermined low speed limit and said skiddingsignal is not present; and means for engaging one of said first orsecond automatically engageable gear ratio operation states of saidtransmission in response to said gear engagementsignal..Iaddend..Iadd.13. The device of claim 12 including:means forsensing engine speed and producing an RPM signal corresponding thereto;means for producing a gear ratio signal corresponding to a ratio of saidRPM signal and said vehicle speed signal; and wherein said means forengaging actuates said second automatically engageable gear ratiooperation state when said speed signal is above a maximum speed limit,said second automatically engageable gear ratio state being the highestgear ratio of said manual/automatic transmission..Iaddend..Iadd.14. Thedevice of claim 13 further including means for fueling the engine to asynchronous RPM speed in response to said RPM signal wherein saidsynchronous RPM speed is mathematically determined from said speedsignal and from a final drive ratio of the transmission corresponding tosaid first or said second gear ratio operation state of thetransmission..Iaddend..Iadd.15. The device of claim 13 wherein saidmeans for engaging includes a solenoid actuator for operably engagingsaid first or said second gear ratio operation state of thetransmission..Iaddend..Iadd.16. The device of claim 15 wherein saidmeans for producing a gear engagement signal and said means for fuelingthe engine are components of an engine controlcomputer..Iaddend..Iadd.17. A method of controlling gearengagement/disengagement of a manual/automatic transmission that iscoupled to an engine, the transmission including a manual mode ofoperation having a plurality of manually selectable gear ratio operationstates and an automatic mode of operation having first and secondautomatically selectable gear ratio operation states, the methodcomprising the steps of:sensing vehicle speed and producing a vehiclespeed signal corresponding thereto; producing a skidding signal inresponse to an abrupt decrease in said vehicle speed signal; producing agear engagement signal when the transmission is in the automatic mode ofoperation in combination with said speed signal being above apredetermined first speed limit and an absence of said skidding signal;and engaging one of said first or second gear ratio operation states ofthe transmission in response to said gear engagementsignal..Iaddend..Iadd.18. The method of claim 17 wherein said first orsaid second gear ratio operation states are engaged in response to thefollowing conditions: a) presence of said top gear signal, and b) saidvehicle speed signal exceeding said predetermined first speedlimit..Iaddend..Iadd.19. The method of claim 17 further includes thesteps of:sensing engine speed and producing an engine speed signalcorresponding thereto; and fueling the engine to a synchronous enginespeed prior to said engaging step, wherein said synchronous engine speedis mathematically determined from said vehicle speed signal and from afinal drive ratio of the transmission corresponding to said first orsaid second gear ratio state of the transmission..Iaddend.